In semiconductor manufacturing processes in semiconductor manufacturing factories, various metal hydride gases and various halide gases are used. Those gases are combustible and/or harmful, for which reason in view of the environmental conservation, it should not be permitted that exhaust gases containing the same are discharged directly to an atmosphere, but it is necessary to do any treatment for removing those danger and harmfulness.
As the exhaust gases treatment methods, there are a wet method and a dry method. The former is a treatment method for cleaning the exhaust gas with chemicals. On the other hand, the later is a method for flowing an exhaust gas through a tower filled with solid-particles of a treatment agent to cause a chemical function of a harm-removal-requested gas and the treatment agent, namely an absorption reaction and/or a chemical reaction for separation and harm-removal of the dangerous and harmful gas, and it is often used in the treatment for the metal-hydride-containing exhaust gas or the metal halide-containing exhaust gas.
As the solid-particle treatment agent, there have been used a support supporting salts, and particles of metal hydroxide or metal carbonates. At the present, many metal components are disclosed. However, of those treatment agents, the ability of removing the harm from the metal-hydride-containing gas depends on the chemical function between the treatment agent and the metal-hydride-containing gas, for which reason the ability is not permanent. Accordingly, for the actual practice, it is necessary to take a counter-measure for previously detecting any drop of the treatment ability for exchanging with a new treatment agent before the loss of its ability, or flow an exhaust gas through a separately-prepared-tower filled with the treatment agent which will alternatively be exchanged with another of the plural towers.
There appear many patents for the treatment agent for the metal-hydride-containing exhaust gas. For example, the treatment agents comprising metal hydroxide, metal carbonate, and basic metal carbonate are disclosed in Japanese laid-open patent publications Nos. 05-284847, 06-319945, and 08-192024 and Japanese patent publication No. 05-61966.
Those treatment agents disclosed in those patents use a commercially available metal hydroxide as a metal compound, or use a metal hydroxide obtained by a neutralization reaction between metal salts and alkali hydroxide, or use a commercially available metal carbonate as a metal compound, or use a basic metal carbonate obtained by a neutralization reaction between metal salts and alkali carbonate. Those metal compounds are subjected to a sole use or a combined use with various inorganic compounds such as alumina, silica, heavy metal compounds, titanium oxide and soda-lime for improvement in physical or chemical properties of the metal compounds.
For example, Japanese Patent No. 2926459 discloses the treatment agent as the metal hydroxide, wherein either a commercially available copper hydroxide or a copper hydroxide obtained by a neutralization reaction between copper salt and alkali hydroxide is added with a stabilizing agent of a variety of metal compound.
Japanese Patent Publication No. 5-61966 discloses a treatment agent using a basic copper carbonate as a metal compound. The treatment agent is produced by dry or wet sprinkling, over soda-lime, the basic copper carbonate prepared by the neutralization between copper salts and alkali carbonates.
Japanese patent No. 2604991 discloses a treatment agent using a basic copper carbonate as a metal compound. The treatment agent has been produced as follows. A neutralization reaction between copper salts solution and a sodium carbonate solution is made to obtain a basic copper carbonate which is then subjected to a wet mixture with an anatase-type titanium dioxide for subsequent molding process. The basic copper carbonate is such a compound that if a compound expressed by a molecular formula CuCO3Cu(OH)2 is obtained by a precipitation in a state that pH-value is neutral or weak alkali, then an amount of OH-group contained in the obtained compound is not less than 1.1 times of it.
Japanese laid-open patent publication No. 8-192024 discloses that a metal carbonate or a metal basic carbonate comprises at least one kind of metal carbonate or metal basic carbonate which is selected from the group consisting of Cu, Zn, Mn, Fe, Co and Ni, and this metal carbonate or metal basic carbonate is available as an agent or an industrial chemical, or is produced from the corresponding metal salts solution by an ordinal measure. It is also disclosed that the metal carbonate or the metal basic carbonate are molded to form a treatment agent.
Japanese laid-open patent publications Nos. 10-235185 and 11-019475 disclose treatment agents of metal oxides, which main component is an oxide selected from two or more metal oxides, for example, copper oxide, silver oxide, manganese dioxide, and is capable of harm-removal of an exhaust gas containing a large amount of a high concentration metal hydride gas at an ordinal temperature.
In the above publication, it is also disclosed that in case that the metal compound is hydroxide or carbonates, then its color change appears by an adsorption of the harm-removing gas and/or a chemical reaction with the harm-removing gas, for which reason color change of the treatment agent may be viewed or monitored to detect a residual harm-removing performance of the treatment agent. The treatment agent serves as a detecting agent for detecting a leakage of the metal hydride gas in addition to the role of the treatment agent.
The treatment by the metal compound to the metal hydride containing exhaust gas depends on the adsorption and/or chemical reaction between the treatment agent and the harm-removal-target gas. In order to increase the treatment performance for treating the metal hydride gas by the treatment agent, it is effective to increase the adsorption, the adsorbing capacity and the reactivity. However, the above-described conventional treatment agent comprising the metal hydroxide, the metal carbonate or the metal basic carbonate is merely prepared by molding either the normal industrial chemical or the precipitated compounds, or is merely prepared by mixture with other compounds and subsequent molding process. There resides a possibility of improvement in the performance.
The chemical reactions in the treatments to the exhaust gases are exothermic reactions, for which reason a temperature increase is unavoidable for the treatment to the exhaust gas by the metal compounds. The treatment to the exhaust gas containing the high concentration metal hydride or a large amount of the exhaust gas may cause a possible large temperature increase. For this reason, the treatment is required to show high performance and low heat-generation.
Particularly, if the exhaust gas includes hydrogen, a heat generated in the treatment is accumulated to increase a layer or a bed of the treatment agent, which may give rise a possible reduction reaction of the metal component of the treatment agent with hydrogen. This reduction reaction is also exothermic reaction. The temperature increase is further emphasized, thereby causing a possible change or deterioration in physical property of the metal component of the treatment agent, and further a possible undesired influence to the quality of the material of the exhaust gas treatment system. Accordingly, if the exhaust gas includes hydrogen, then the treatment agent is required not only to show high performance for removing harm but also to cause a low heat generation.